A cylinder, regardless of whether it can be swung out or not, comprises a plurality of chambers each capable of receiving one round or cartridge, and is mounted on a coaxial shaft in an associated housing in the frame of a gun.
It is essential to provide operating clearance between the cylinder and the barrel in order to allow the cylinder to rotate automatically about its axis after each shot, so as to present the projectile guidance and firing mechanism with a new prior-loaded cartridge. This operating clearance is necessary a fortiori in a gun having a cylinder which can be swung out to enable the gun to be loaded by pivoting the cylinder assembly about a pivot axis which is parallel to, but offset from, its axis of symmetry.
It is well-known that the accuracy of firearms depends on numerous factors.
In addition to purely structural factors such as the accuracy of the alignment between the barrel and the associated cylinder, or the state and the rectitude of the rifling in the barrel, shooting accuracy is greatly influenced by the initial speed of the projectile. For a given projectile, i.e. for a given quantity of explosive contained in the tubular casing of the cartridge, this speed depends essentially on the pressure inside the chamber during combustion of the propellant explosive, and thus on the quality of the sealing that must be provided between the combustion chamber and its surroundings.
In all guns using cartridges, rearwards sealing is provided by the tubular casing of the cartridge coming into contact with the adjacent inside wall of the chamber.
In contrast, forwards sealing is provided by the gun mechanism. This forwards sealing is particularly sensitive in cylinder guns since they require operating clearance between the cylinder and the barrel, as recalled above.
One very old technique proposed at the end of the last century by the Nagant brothers relied on the principle of sealing being provided between the tubular casing of the cartridge and the inlet to the barrel.
According to this principle, the round is made to penetrate into the revolver barrel in order to provide a continuous tube: the cylinder is moved forwardly by an actuating pusher connected to the trigger so that the front end of the cartridge casing with the projectile contained therein then penetrates into the rear end of the barrel; when pressure is released, a spring returns the cylinder rearwardly, thereby disengaging the empty cartridge casing from the barrel and enabling the cylinder to be rotated.
This technique, although highly ingenious for the period, nevertheless suffers from major drawbacks. Firstly a step must be provided inside the barrel in order to provide an abutment for the cartridge casing; and this requires special ammunition since the projectile needs to be completely enveloped by the cartridge casing since otherwise the cylinder would have to move an excessive distance axially. Further, this mechanism requires several parts for organizing cylinder displacement in an axial direction and this is disadvantageous both in terms of reliability and in terms of manufacturing costs.
Techniques similar to those of the Nagant brothers are described in British Pat. No. 15 753 (1909) and in German Pat. No. 58 338: both describe moving cylinder systems using an actuator pusher linked to the gun mechanism.
In order to avoid these drawbacks, current techniques seek to reduce the operating clearance between the cylinder and the barrel to as small a value as possible. Careful machining makes it possible to achieve small clearances, for example of the order of a few tenths of a millimeter, however the clearance is never eliminated.
In addition, the presence of this operating clearance means that it is not possible to prevent incandescent particles from escaping through the gap (such hot grains of explosive are often called "back-firing" by persons skilled in the art). It should be observed that this particular drawback is avoided with the above-mentioned Nagant brothers' technique by virtue of the continuous tube principle.
Proposals have also been made to use a sealing ring disposed in the front portion of the cylinder, which ring is projected against the adjacent end of the barrel during firing in order to locally close the gap between the barrel and the front face of the cylinder (see U.S. Pat. No. 3,768,362 for example). Nevertheless these techniques are complicated and expensive (the ring must be made of a high quality material in order to withstand the high temperatures involved).
Finally, the state of the art is also illustrated by systems adapted for cartridge-free rounds for automatic guns: the cylinder is movable along a helical path for loading the breech or for ejecting an unfired round, but said cylinder remains in a single longitudinal firing position (see U.S. Pat. No. 3,889,572, for example).
The aim of the invention is to provide a cylinder firearm, and an associated improved cylinder, suitable for providing very good front sealing between the cylinder and the barrel of the gun, without requiring an actuator mechanism using several moving mechanical parts, and without requiring the use of special ammunition in which the cartridge casing completely covers the projectile.